Carbon-fiber reinforced composites are ideal light-weighting candidates to replace traditional engineering materials. The mechanical performance of these composites results from a complex interplay ...of influences operating over several length and time scales. The mechanical performance may therefore be limited by many factors, one of which being the modest interfacial adhesion between the carbon fiber and the polymer. Chemical modification of the fiber, via surface grafting of molecules, is one possible strategy to enhance interactions across the fiber–polymer interface. To achieve systematic improvements in these modified materials, the ability to manipulate and monitor the molecular structure of the polymer interphase and the surface grafted molecules in the composite is essential, but challenging to accomplish from a purely experimental perspective. Alternatively, molecular simulations can bridge this knowledge gap by providing molecular-scale insights into the optimal design of these surface-grafted molecules to deliver superior mechanical properties. Here we use molecular dynamics simulations to predict the interfacial shear response of a typical epoxy/carbon-fiber composite for both pristine fiber and a range of surface graftings. We allow for the dynamic curing of the epoxy in the presence of the functionalized surface, including cross-link formation between the grafted molecules and the polymer matrix. Our predictions agree with recently reported experimental data for these systems and reveal the molecular-scale origins of the enhanced interfacial shear response arising from functionalization. In addition to the presence of interfacial covalent bonds, we find that the interfacial structural complexity, resulting from the presence of the grafted molecules, and a concomitant spatial homogeneity of the interphase polymer density are beneficial factors in conferring high interfacial shear stress. Our approach paves the way for computational screening processes to design, test, and rapidly identify viable surface modifications in silico, which would enable rapid systematic progress in optimizing the match between the carbon fiber treatment and the desired thermoset polymer matrix.
...a concept goes beyond that of a function for light stimulating specialized retinal ganglion cells to entrain circadian rhythms but extends this to include light having a direct influence on all ...neurons to potentially influence a range of core higher-order brain activities. ...the chlorophyll ingested by animals can be converted into metabolites that become incorporated within mitochondria across a number of body tissues. ...other wavelengths across the light spectrum have been reported to be absorbed by yet other chromophores. From a transcranial approach, light can penetrate down to the level of the cerebral cortex (Hamblin, 2016; Mitrofanis, 2019). ...light, being an electromagnetic wave, can potentially influence the activity and frequency of neurons in the large-scale neural networks, for example to influence the functional connectivity within the default mode network, as well as within and with the other networks, such as the central executive and salience ones Figure 1B. The significance of why light would have such an effect on these networks perhaps subserves a key survival strategy for the organism.
Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross‐linkers. These polymers have been used in a variety of applications such as energy ...storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of these advances, there is a need for methods to recycle and reprocess these polymers. In this study, polymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanical compression. Upon heating these molds at relatively low temperatures (≈100 °C), chemical bonding occurs at the polymer interfaces by S−S metathesis. This method of processing is distinct from previous studies on inverse vulcanization because the polymers examined in this study do not form a liquid phase when heated. Neither compression nor heating alone was sufficient to mold these polymers into new architectures, so this is a new concept in the manipulation of sulfur polymers. Additionally, high‐level ab initio calculations revealed that the weakest S−S bond in organic polysulfides decreases linearly in strength from a sulfur rank of 2 to 4, but then remains constant at about 100 kJ mol−1 for higher sulfur rank. This is critical information in engineering these polymers for S−S metathesis. Guided by this insight, polymer repair, recycling, and repurposing into new composites was demonstrated.
Under pressure: The reactive interfaces of rubber polysulfides made by inverse vulcanization bond together when heated with compression. The S−S metathesis reaction occurs at relatively low temperature and allows additive assembly, recycling, and repurposing of these materials, as well as the preparation of composites.
Here we report on the role of oxygen in the evolution of radial heterogeneity in the fibre structure and properties of PAN fibres stabilized in air and vacuum at different temperatures. Modulus ...mapping by Nano-indentation showed heterogeneous modulus distribution in the fibres treated in air, while no variation in modulus was observed in fibres processed in vacuum. Raman spectroscopy and elemental analysis revealed that the temperature dependent oxygen diffusion from skin to core of the fibres assisted in the evolution of higher extent of sp2-hybridized carbons in the skin compared to core of the air treated samples. Conversely, no radial structure variations were observed in the vacuum treated fibres. Higher modulus in the skin of air-treated fibres was due to the formation of compact structures which was associated with the enhanced intermolecular interactions facilitated by the formation of C=C bonds within the polymer backbone, promoted by oxidative-dehydrogenation reaction. Supporting these observations, the fracture morphology examined by SEM showed a brittle fracture in the skin and ductile fracture in the core.
Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal ...catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.
This paper examines the effect on interfacial shear strength (IFSS) when grafting polyethyleneoxide (PEO) polymers of various molecular weights to a carbon fiber surface. Using copper-azide-alkyne ...cycloaddition click chemistry, PEO polymers of 1 kDa, 2 kDa, 5 kDa, and 10 kDa were tethered to the fiber surface without causing degradation of the fiber surface. The resulting IFSS increases were maximised (130% and 160%) for the 1 kDa and 10 kDa surface modified fibers, respectively. These data suggest that increases in IFSS are the result of an interplay between the density of surface modification versus the penetration of the grafted polymer into the matrix interphase. The trade-off between interphase penetration and surface grafting density is highlighted for the 2 and 5 kDa PEO chains on the fiber surface which display smaller IFSS increases (85% and 117%, respectively). Measuring the mobility of the PEO polymers by 1H NMR found an order of magnitude decrease in diffusion coefficient for each successive increase in molecular weight, supporting the hypothesis that grafting density decreases with molecular weight. Molecular dynamics simulations of the carbon fiber-matrix interface further supports these observations. These results will inform the design of complementary interfaces for various materials in a range of supporting media.
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We review our recent data obtained on the cortical and subcortical components of the human sympathetic connectome - the network of regions involved in the sympathetic control of blood pressure. ...Specifically, we functionally identified the human homologue of the rostral ventrolateral medulla (RVLM), the primary premotor sympathetic nucleus in the medulla responsible for generating sympathetic vasoconstrictor drive. By performing functional magnetic resonance imaging (fMRI) of the brain at the same time as recording muscle sympathetic nerve activity (MSNA), via a microlectrode inserted into the common peroneal nerve, we are able to identify areas of the brain involved in the generation of sympathetic outflow to the muscle vascular bed, a major contributor to blood pressure regulation. Together with functional connectivity analysis of areas identified through MSNA-coupled fMRI, we have established key components of the human sympathetic connectome and their roles in the control of blood pressure. Whilst our studies confirm the role of lower brainstem regions such as the NTS, CVLM and RVLM in baroreflex control of MSNA, our findings indicate that the insula – hypothalamus – PAG – RVLM circuitry is tightly coupled to MSNA at rest. This fits with data obtained from experimental animals, but also emphasizes the role of areas above the brainstem in the regulation of blood pressure.
•We review our recent data obtained on the cortical and subcortical components of the human sympathetic connectome.•We performed fMRI of the brain at the same time as recording muscle sympathetic nerve activity (MSNA) via a microlectrode inserted into a peripheral nerve.•This allows us to identify areas of the brain involved in the generation of sympathetic outflow to the muscle vascular bed.•Our studies emphasize the contributions of areas above the brainstem in the regulation of blood pressure.
Background
Migraine is a neurological disorder characterized by intense, debilitating headaches, often coupled with nausea, vomiting and sensitivity to light and sound. Whilst changes in sensory ...processes during a migraine attack have been well-described, there is growing evidence that even between migraine attacks, sensory abilities are disrupted in migraine. Brain imaging studies have investigated altered coupling between areas of the descending pain modulatory pathway but coupling between somatosensory processing regions between migraine attacks has not been properly studied. The aim of this study was to determine if ongoing functional connectivity between visual, auditory, olfactory, gustatory and somatosensory cortices are altered during the interictal phase of migraine.
Methods
To explore the neural mechanisms underpinning interictal changes in sensory processing, we used functional magnetic resonance imaging to compare resting brain activity patterns and connectivity in migraineurs between migraine attacks (
n
= 32) and in healthy controls (
n
= 71). Significant differences between groups were determined using two-sample random effects procedures (
p
< 0.05, corrected for multiple comparisons, minimum cluster size 10 contiguous voxels, age and gender included as nuisance variables).
Results
In the migraine group, increases in infra-slow oscillatory activity were detected in the right primary visual cortex (V1), secondary visual cortex (V2) and third visual complex (V3), and left V3. In addition, resting connectivity analysis revealed that migraineurs displayed significantly enhanced connectivity between V1 and V2 with other sensory cortices including the auditory, gustatory, motor and somatosensory cortices.
Conclusions
These data provide evidence for a dysfunctional sensory network in pain-free migraine patients which may be underlying altered sensory processing between migraine attacks.
Solvate Ionic Liquids (SILs) are a relatively new class of ionic liquids consisting of a coordinating solvent and salt, that give rise to a chelate complex with very similar properties to ionic ...liquids. Herein is the exploration of the reported Kamlet-Taft parameters, Gutmann Acceptor numbers and the investigation of chelating effects through NMR spectroscopy of multiple atomic nuclei. These properties are related to the application of SILs as reaction media for organic reactions. This area is also reviewed here, including the implication in catalysis for the Aldol and Kabachnik-Fields reactions and electrocyclization reactions such as Diels-Alder and 2+2 cycloaddition. Solvate ILs exhibit many interesting properties and hold great potential as a solvent for organic transformations.
Carbon fibres with redox-active surface functionalities have shown potential applications in environmental remediation, and as burgeoning materials for structural batteries and super capacitors. In ...this work we describe the tethering of anthraquinone, capable of a reversible 2 electron transfer in aqueous medium, to the carbon fibre surface, and the corresponding effect on interfacial adhesion. The anthraquinone alone results in a >150% improvement in interfacial shear strength and the redox activity is preserved. Further to this, we then use this conductive film as a means to grow an acrylic acid polymer on top of the anthraquinone base layer, characterized by water contact angle, infrared spectroscopy, and depth-profiling X-ray photoelectron spectroscopy. This outermost layer imparts additional benefit to fibre-to-matrix adhesion and preserves the redox activity of the modified carbon fibers. This work demonstrates the ability to grow dual component and covalently-attached sizings to the carbon fiber surface, without compromising the inherent benefits of the underlying carbon fibers.
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